Wow, I read this entire thread and I have to say I am amazed. My husband and I have no children, but I am the aunt to three and the great-aunt to two more all girls and all love to play and have fun. I was a Montessori pre-primary teacher for three years.
Now, that said here is what I feel about the idea of swords, guns, or princess wands.
1. WDW is a place for kids to be kids. I agree children should be allowed to play and have fun. Most definitely, however, if a childs play injurs another child or adult than that play needs to stop. No child should be allowed to stab or hit a complete stranger with any item, be it sword, gun, or princess wand. It's just rude. That being said sometimes accidents happen, an unintentional hit occurs. I would expect that the child say to "sorry" and I would expect the parent or parents of the child to educate the child on why it is not ok to hit a perfect stranger.
2. Children need boundaries. As a child I know my parent set very good boundaries. They took me to WDW many times and they loved to see me skip through the park and to play but if my play in any way negatively effected another individual my parents would take the lead and explain to me what needed to be changed. We take the same path with our beautiful nieces.
One of our lovely nieces decided that it was perfectly ok to throw a ball at her loving uncles head as he was resting on the couch. The ball was immediately taken away and the young niece learned that throwing the ball in that manner would not be tolerated. Boundaries are important.
3. On a side note, some of the posts seem to indicate that getting hit with a plastic sword or knife is not going to cause any really injury. As a person who bruises easily due to a disability I have to say that this thinking is flawed. I can get "injured" by a seatbelt fitting to tightly or by scraping against a door frame. I would definitely get "injured" if a random child was to run up to me and stab me. I also feel that the idea of "oh it won't hurt someone" as an excuse to allow a child to stab or hit a stranger is also flawed.
So, if you feel the need to flame please be my guest.